Illumination optical apparatus and projection exposure apparatus

ABSTRACT

An illumination optical apparatus and projection exposure apparatus capable of reducing a light quantity loss when a mask is illuminated with a polarized illumination light. An illumination optical system for illuminating a reticle with an illumination light and a projection optical system for projecting the pattern image of the reticle onto a wafer are provided. An illumination light emitted from an exposure light source in a linearly polarized state in the illumination optical system passes through first and second birefringent members having different fast axis directions and is converted into a polarized state that is substantially linearly polarized in a circumferential direction with the optical axis as the center in an almost specific annular area, and them illuminates the reticle under an annular illuminating condition after passing through a fly-eye lens.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.11/410,952, filed Apr. 26, 2006, which is a Continuation-in-part ofPCT/JP2004/015853 filed Oct. 26, 2004. This application claims thebenefit of Japanese Patent Application No. 2003-367963, filed Oct. 28,2003. The entire disclosures of the prior applications are herebyincorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to illumination technology and exposuretechnology used in the lithography step for fabricating various devices,e.g., semiconductor integrated circuits (LSI and the like), image pickupdevices, or liquid crystal displays and, more particularly, toillumination technology and exposure technology for illuminating a maskpattern with light in a predetermined polarization state. Furthermore,the present invention relates to device fabrication technology using theexposure technology.

2. Related Background Art

For forming microscopic patterns of electronic devices such assemiconductor integrated circuits or liquid crystal displays, a methodadopted is to project a demagnified image of a pattern on a reticle (ora photomask or the like) as a mask on which the pattern to be formed isdrawn at a proportional magnification of about 4-5 times, through aprojection optical system onto a wafer (or glass plate or the like) as asubstrate to be exposed (photosensitive body) to effect exposure andtransfer of the image. Projection exposure apparatus used for theexposure and transfer include those of a stationary exposure type suchas steppers, and those of a scanning exposure type such as scanningsteppers. The resolution of the projection optical system isproportional to a value obtained by dividing an exposure wavelength by anumerical aperture (NA) of the projection optical system. The numericalaperture (NA) of the projection optical system is given by multiplying asine (sin) of a maximum angle of incidence of illumination light forexposure onto the wafer, by a refractive index of a medium through whichthe light passes.

Therefore, in order to meet the demand for miniaturization of thesemiconductor integrated circuits and others, the exposure wavelength ofthe projection exposure apparatus has been decreased toward shorterwavelengths. The mainstream exposure wavelength at present is 248 nm ofKrF excimer laser, and the shorter wavelength of 193 nm of ArF excimerlaser is also close to practical use. There are also proposals on theprojection exposure apparatus using exposure light sources in theso-called vacuum ultraviolet region such as the F₂ laser with the muchshorter wavelength of 157 nm and the Ar₂ laser with the wavelength of126 nm. Since it is also possible to achieve a higher resolution by alarger numerical aperture (larger NA) of the projection optical systeminstead of the use of shorter wavelength, there are also attempts todevelop the projection optical system with a much larger NA, and theleading NA of the projection optical system at present is approximately0.8.

On the other hand, there are also practically available techniques toenhance the resolution of the pattern to be transferred, even with useof the same exposure wavelength and the projection optical system withthe same NA, so called super resolution techniques, such as a methodusing a so-called phase shift reticle, and annular illumination, dipoleillumination, and quadrupole illumination to control angles of incidenceof the illumination light onto the reticle in a predetermineddistribution.

Among those, the annular illumination is to limit the incidence anglerange of illumination light onto the reticle to predetermined angles,i.e., to limit the distribution of illumination light on the pupil planeof the illumination optical system to within a predetermined annularregion centered on the optical axis of the illumination optical system,thereby offering the effect of improvement in the resolution and depthof focus (e.g., reference is made to Japanese Patent ApplicationLaid-Open No. 61-91662). On the other hand, the dipole illumination andquadrupole illumination are applied to cases where the pattern on thereticle is one with specific directionality, and are arranged to limit,as well as the incidence angle range, the direction of incidence of theillumination light to a direction suitable for the directionality of thepattern, thereby achieving great improvement in the resolution and depthof focus (e.g., reference is made to Japanese Patent ApplicationLaid-Open No. 4-101148 or U.S. Pat. No. 6,233,041 equivalent thereto andto Japanese Patent Application Laid-Open No. 4-225357 or U.S. Pat. No.6,211,944 equivalent thereto).

There are other proposals of attempts to optimize the polarization stateof the illumination light relative to the direction of the pattern onthe reticle, thereby achieving improvement in the resolution and depthof focus. This method is to convert the illumination light into linearlypolarized light with the polarization direction (direction of theelectric field) along a direction orthogonal to the periodic directionof the pattern, i.e., along a direction parallel to the longitudinaldirection of the pattern, thereby achieving improvement in contrast andothers of the transferred image (e.g., Japanese Patent ApplicationLaid-Open No. 5-109601 and Thimothy A. Brunner, et al.: “High NALithographic imaging at Brewster's angle,” SPIE (USA) Vol. 4691, pp.1-24 (2002).

Concerning the annular illumination, there are also proposals ofattempts to match the polarization direction of the illumination lightin an annular region in which the illumination light is distributed onthe pupil plane of the illumination optical system, with thecircumferential direction of the annular region, thereby achievingimprovement in the resolution, contrast, etc. of the projected image.

In effecting the annular illumination by the conventional technology asdescribed above, there was the problem of large loss in quantity of theillumination light to lower illumination efficiency if the polarizationstate of the illumination light was made to be linear polarizationsubstantially matched with the circumferential direction of the annularregion on the pupil plane of the illumination optical system.

Specifically, the illumination light emitted from the recentlymainstream narrow-band KrF excimer laser source is uniform, linearlypolarized light. If the light is kept in that polarization state andguided to the reticle, the reticle will be illuminated with the uniform,linearly polarized light, and it is thus needless to mention that it isinfeasible to obtain the linearly polarized light with the polarizationdirection matched with the circumferential direction of the annularregion on the pupil plane of the illumination optical system asdescribed above.

Therefore, in order to realize the aforementioned polarization state, itwas necessary to adopt, for example, a method of converting the linearlypolarized light emitted from the light source, once into randomlypolarized light and thereafter, in each part of the annular region,selecting a desired polarization component from the illumination lightof random polarization, using a polarization selecting element such as apolarization filter or a polarization beam splitter. This method usedonly energy in the predetermined linear polarization component out ofthe energy of the illumination light of random polarization, i.e., onlyapproximately half energy as the illumination light onto the reticle,and thus posed the problem of large loss in quantity of the illuminationlight and large loss in exposure power on the wafer in turn, resultingin reduction in processing performance (throughput) of the exposureapparatus.

Similarly, in application of multipole illumination such as the dipoleillumination or quadrupole illumination, there was also the problem ofreduction in illumination efficiency if the polarization of theillumination light in each dipole or quadrupole region was attempted tobe set in a predetermined state on the pupil plane of the illuminationoptical system.

SUMMARY OF THE INVENTION

Reference symbols in parentheses attached to respective elements of thepresent invention below correspond to configurations of embodiments ofthe present invention described later. It is, however, noted that eachreference symbol is only an example of an element corresponding theretoand is by no means intended to limit each element to the configurationsof the embodiments.

A first aspect of the present embodiment is to provide a projectionexposure apparatus for projecting a pattern image on a first object on asecond object, the projection exposure apparatus comprising: aprojection optical system for projecting the image of pattern on thefirst object on the second object; and an illumination optical systemfor illuminating a first object with illumination light from a lightsource, and comprising at least two birefringent members arranged alonga traveling direction of the illumination light, wherein a direction ofa fast axis of at least one birefringent member out of the birefringentmembers is different from a direction of a fast axis of the otherbirefringent member, and wherein a specific illumination beam incidentin a specific incidence angle range to the first object among theillumination light generated in a substantially single polarizationstate from the light source is light in a polarization state consistingprimarily of S-polarization.

A second aspect of the present embodiment is to provide a projectionexposure apparatus for projecting an image of a pattern on a firstobject onto a second object, comprising: a projection optical system forprojecting the image of the pattern on the first object onto the secondobject; and an illumination optical system for illuminating the firstobject with light supplied from an outside light source, theillumination optical system comprising a diffractive optical element anda birefringent member arranged in order along a traveling direction ofthe light.

A third aspect of the present embodiment is to provide an illuminationoptical apparatus for illuminating a first object with illuminationlight from a light source, comprising: at least two birefringent membersarranged along a traveling direction of the illumination light, whereina direction of a fast axis of at least one birefringent member out ofthe birefringent members is different from a direction of a fast axis ofthe other birefringent member, and wherein a specific illumination beamincident in a specific incidence angle range onto the first object amongthe illumination light in a substantially single polarization statesupplied from the light source is light in a polarization stateconsisting primarily of S-polarization.

A fourth aspect of the present invention is to provide an illuminationoptical apparatus for illuminating a first object with illuminationlight from a light source, comprising: a diffractive optical element anda birefringent member arranged in order along a traveling direction ofthe illumination light.

A fifth aspect of the embodiments is to provide an exposure method usingthe above projection exposure apparatus according to the aboveembodiments.

A sixth aspect of the embodiments is to provide a method of making adevice using the exposure method according to the above embodiments.

According to the present embodiments, for example, thicknesses of thebirefringent members are set in their respective predetermineddistributions, whereby the polarization after passage of theillumination light emitted from the light source, through the pluralityof birefringent members, can be, for example, in a state consistingprimarily of polarization in the circumferential direction around theoptical axis in an annular region centered around the optical axis. Anexit surface of the birefringent members is located, for example, at aposition near the pupil plane of the illumination optical system,whereby the first object is illuminated with the illumination light(specific illumination beam) having passed through the annular regionand kept in the predetermined polarization state consisting primarily ofS-polarization, with little loss in quantity of light.

In this case, the apparatus may comprise a beam limiting member (9 a, 9b) for limiting the illumination light incident to the first object, tothe specific illumination beam. This makes the first object illuminatedunder the condition of almost annular illumination. When in this annularillumination the illumination light is almost S-polarization on thefirst object, a projected image of a line-and-space pattern arranged ata fine pitch in an arbitrary direction on the first object is formedmainly by the illumination light with the polarization directionparallel to the longitudinal direction of the line pattern and,therefore, improvement is made in imaging characteristics such as thecontrast, resolution, and depth of focus.

The beam limiting member may be configured to further limit thedirection of incidence of the illumination light incident to the firstobject, to a plurality of specific, substantially discrete directions.Since this implements illumination such as the dipole illumination orquadrupole illumination, improvement is made in imaging characteristicsof a line-and-space pattern arranged at a fine pitch in a predetermineddirection.

The present invention will be more fully understood from the detaileddescription given hereinbelow and the accompanying drawings, which aregiven by way of illustration only and are not to be considered aslimiting the embodiment.

Further scope of applicability of the embodiment will become apparentfrom the detailed description given hereinafter. However, it should beunderstood that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the invention will be apparent to those skilled inthe art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing a schematic configuration of a projectionexposure apparatus, partly cut, as an example of an embodied form of thepresent invention.

FIG. 2A is a view of birefringent member 12 in FIG. 1, viewed to +Ydirection,

FIG. 2B a sectional view along line AA′ in FIG. 2A.

FIG. 3A is a view of birefringent member 13 in FIG. 1, viewed to +Ydirection,

FIG. 3B a sectional view along line BB′ in FIG. 3A.

FIG. 4A is a diagram showing an example of relationship betweenpolarization phase difference ΔP1 and position X in the firstbirefringent member 12.

FIG. 4B is a diagram showing an example of relationship betweenpolarization phase difference ΔP2 and position XZ in the secondbirefringent member 13.

FIG. 4C a drawing showing an example of polarization states ofillumination light emerging from the second birefringent member 13.

FIG. 5 is a drawing showing an example of polarization states ofillumination light emerging from the first birefringent member 12.

FIG. 6A is a diagram showing another example of relationship betweenpolarization phase difference ΔP1 and position X in the firstbirefringent member 12.

FIG. 6B a diagram showing another example of relationship betweenpolarization phase difference ΔP2 and position XZ in the secondbirefringent member 13.

FIG. 6C a drawing showing another example of polarization states ofillumination light emerging from the second birefringent member 13.

FIG. 7A is a plan view showing an example of microscopic periodicpattern PX formed on reticle R of FIG. 1.

FIG. 7B a drawing showing a distribution of diffracted light formed inpupil plane 26 of the projection optical system when the pattern of FIG.7A is illuminated under a predetermined condition.

FIG. 7C a drawing showing a condition for annular illumination forilluminating the pattern PX of FIG. 7A.

FIG. 8A is a perspective view showing a simplified relation betweenpupil plane 15 of illumination optical system ILS and reticle R in FIG.1.

FIG. 8B a view of a part of FIG. 8A viewed to +Y direction.

FIG. 8C a view of part of FIG. 8A viewed to −X direction.

FIG. 9 is a drawing showing a plurality of conical prisms that can bedisposed between birefringent members 12, 13 and fly's eye lens 14 inFIG. 1, for making the radius of the specific annular region variable,in an example of the embodied form of the present invention.

FIG. 10 is a drawing showing an example of a polarization controloptical system that can be disposed at the position of polarizationcontrolling member 4 in FIG. 1.

FIG. 11 is a drawing showing an example of a lithography step forfabricating semiconductor devices by use of the projection exposureapparatus according to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An example of preferred embodiment of the present invention will bedescribed below with reference to the drawings. The present example isan application of the present invention to a case where exposure isperformed by a projection exposure apparatus of the scanning exposuretype (scanning stepper) according to the step-and-scan method.

FIG. 1 is a drawing showing a schematic configuration of the projectionexposure apparatus of the present example partly cut, and in this FIG. 1the projection exposure apparatus of the present example is providedwith an illumination optical system ILS and a projection optical system25. The former illumination optical system ILS is provided with aplurality of optical members arranged along the optical axis (opticalaxis of illumination system) AX1, AX2, AX3 from an exposure light source1 (light source) to a condenser lens 20 (the details of which will bedescribed later), and illuminates an illumination field on a patternsurface (reticle surface) of reticle R as a mask under a uniformilluminance distribution with illumination light for exposure (exposurelight) IL as an exposure beam from the exposure light source 1. Thelatter projection optical system 25 projects a demagnified image at aprojection magnification M (where M is a demagnification rate, e.g., ¼or ⅕) of a pattern in the illumination field on the reticle R, under theillumination light into an exposure region on one shot area on a wafer Wcoated with a photoresist, as a substrate to be exposed (substrate) oras a photosensitive body. The reticle R and wafer W can also be regardedas a first object and as a second object, respectively. The wafer W is,for example, a substrate of disk shape with the radius of about 200-300mm of a semiconductor (silicon or the like) or SOI (silicon oninsulator) or the like. The projection optical system 25 of the presentexample is, for example, a dioptric system, but can also be acatadioptric system or the like.

In the description hereinafter, a coordinate system as to the projectionoptical system 25, reticle R, and wafer W is defined as follows in FIG.1: the Z-axis is taken in parallel with the optical axis AX4 of theprojection optical system 25, the Y-axis along the scanning direction ofreticle R and wafer W (direction parallel to the plane of FIG. 1) duringscanning exposure in the plane (XY plane) perpendicular to the Z-axis,and the X-axis along the non-scanning direction (direction normal to theplane of FIG. 1). In this case, the illumination field on the reticle Ris a region elongated in the X-direction being the non-scanningdirection, and an exposure region on the wafer W is an elongated regionconjugate with the illumination field. The optical axis AX4 of theprojection optical system 25 agrees with the optical axis ofillumination system AX3 on the reticle R.

First, the reticle R on which a pattern to be transferred by exposure isformed, is stuck and held on a reticle stage 21, and the reticle stage21 moves at a constant speed in the Y-direction on a reticle base 22 andfinely moves in the X-direction, in the Y-direction, and in therotational direction about the Z-axis so as to compensate for asynchronization error, to effect scanning of reticle R. TheX-directional and Y-directional positions and the angle of rotation ofthe reticle stage 21 are measured by means of moving mirror 23 providedthereon, and laser interferometer 24. Based on measurements of the laserinterferometer and control information from main control system 34, areticle stage driving system 32 controls the position and speed ofreticle stage 21 through a driving mechanism (not shown) such as alinear motor. A reticle alignment microscope (not shown) for reticlealignment is disposed above the marginal region of the reticle R.

On the other hand, the wafer W is stuck and held through a wafer holder(not shown) on a wafer stage 27, and the wafer stage 27 is mounted on awafer base 30 so that it can move at a constant speed in the Y-directionand achieve step movement in the X-direction and in the Y-direction. Thewafer stage 27 is also provided with a Z-leveling mechanism for aligningthe surface of wafer W with the image plane of the projection opticalsystem 25, based on measurements of an unrepresented autofocus sensor.The X-directional and Y-directional positions and the angle of rotationof the wafer stage 27 are measured by means of moving mirror 28 providedthereon, and laser interferometer 29. Based on measurements of the laserinterferometer and control information from main control system 34, awafer stage driving system 33 controls the position and speed of thewafer stage 27 through a driving mechanism (not shown) such as a linearmotor. For wafer alignment, an alignment sensor 31 of the off-axismethod and, for example, the FIA (Field Image Alignment) method fordetecting positions of marks for alignment on the wafer W is disposed inthe vicinity of the projection optical system 25.

Prior to exposure by the projection exposure apparatus of the presentexample, alignment of the reticle R is carried out with theaforementioned reticle alignment microscope, and alignment of the waferW is carried out by detecting the positions of the positioning marksformed along with a circuit pattern in a previous exposure step on thewafer W, by means of the alignment sensor 31. After that, the apparatusrepeatedly carries out the operation of driving the reticle stage 21 andwafer stage 27 in a state in which the illumination light IL illuminatesthe illumination field on the reticle R, to synchronously scan thereticle R and one shot area on the wafer W in the Y-direction, and theoperation of terminating emission of the illumination light IL anddriving the wafer stage 27 to effect step movement of the wafer W in theX-direction and in the Y-direction. A ratio of scanning speeds of thereticle stage 21 and the wafer stage 27 during the synchronous scanningis equal to a projection magnification M of the projection opticalsystem 25, in order to keep the imaging relation between the reticle Rand the wafer W through the projection optical system 25. Theseoperations result in effecting exposure to transfer the pattern image ofthe reticle R into all the shot areas on the wafer W by thestep-and-scan method.

Next, a configuration of the illumination optical system ILS of thepresent example will be described in detail. In FIG. 1, an ArF (argonfluorine) excimer laser (wavelength 193 nm) is used as the exposurelight source 1 of the present example. The exposure light source 1 canalso be another laser light source, e.g., a KrF (krypton fluorine)excimer laser (wavelength 248 nm), an F₂ (fluorine molecule) laser(wavelength 157 nm), or a Kr₂ (krypton molecule) laser (wavelength 146nm). These laser light sources (including the exposure light source 1)are narrow-band lasers or wavelength-selected lasers, and theillumination light IL emitted from the exposure light source 1 is in apolarization state consisting primarily of linear polarization becauseof the narrowing of band or wavelength selection. In the descriptionhereinafter, it is assumed that in FIG. 1 the illumination light ILimmediately after emitted from the exposure light source 1 consistsprimarily of linearly polarized light whose polarization direction(direction of the electric field) coincides with the X-direction in FIG.1.

The illumination light IL emitted from the exposure light source 1travels along the optical axis of illumination system AX1 and throughrelay lenses 2, 3 to enter a polarization controlling member 4 (detailedlater) as a polarization controlling mechanism. The illumination lightIL emerging from the polarization controlling member 4 travels through azoom optical system (5, 6) consisting of a combination of a concave lens5 and a convex lens 6, and is then reflected by a mirror 7 for bendingof optical path to enter a Diffractive Optical Element (DOE) 9 a alongthe optical axis of illumination system AX2. The diffractive opticalelement 9 a is comprised of a phase type diffraction grating, and theillumination light IL incident thereto travels as diffracted intopredetermined directions.

As described later, a diffraction angle and direction of each diffractedlight from the diffractive optical element 9 a as a beam limiting membercorrespond to a position of the illumination light IL on the pupil plane15 of the illumination optical system ILS and to an angle and directionof incidence of the illumination light IL to the reticle R. A pluralityof diffractive optical elements, including the diffractive opticalelement 9 a and another diffractive optical element 9 b with differentdiffraction action, are arranged on a member 8 of turret shape. Theapparatus is constructed for example as follows: the member 8 is drivenby a replacing mechanism 10 under control of the main control system 34to load the diffractive optical element 9 a or the like at an arbitraryposition on the member 8 to the position on the optical axis ofillumination system AX2, whereby the incidence angle range and directionof the illumination light to the reticle R (or the position of theillumination light on the pupil plane 15) can be set to a desired rangein accordance with the pattern of the reticle R. The incidence anglerange can also be finely adjusted supplementarily by moving each of theconcave lens 5 and the convex lens 6 constituting the aforementionedzoom optical system (5, 6) in the direction of the optical axis ofillumination system AX1.

The illumination light (diffracted light) IL emerging from thediffractive optical element 9 a travels along the optical axis ofillumination system AX2 and through relay lens 11 to successively enterthe first birefringent member 12 and second birefringent member 13 beingthe plurality of birefringent members in the present invention. Thedetails of these birefringent members will be described later. In thepresent embodiment, a fly's eye lens 14 being an optical integrator(illuminance uniforming member) is disposed behind the birefringentmember 13. The illumination light IL emerging from the fly's eye lens 14travels via relay lens 16, field stop 17, and condenser lens 18 to amirror 19 for bending of optical path, and the illumination light ILreflected thereon then travels along the optical axis of illuminationsystem AX3 and through condenser lens 20 to illuminate the reticle R.The pattern on the reticle R illuminated in this manner is projected andtransferred onto the wafer W by the projection optical system 25 asdescribed above.

It is also possible to construct the field stop 17 as a scanning type,if necessary, and to effect scanning thereof in synchronization with thescanning of the reticle stage 21 and wafer stage 27. In this case, thefield stop may be constructed of separate components of a fixed fieldstop and a movable field stop.

In this configuration, the exit-side surface of the fly's eye lens 14 islocated near the pupil plane 15 of the illumination optical system ILS.The pupil plane 15 acts as an optical Fourier transform plane withrespect to the pattern surface (reticle surface) of the reticle Rthrough the optical members (relay lens 16, field stop 17, condenserlenses 18, 20, and mirror 19) in the illumination optical system ILSfrom the pupil plane 15 to the reticle R. Namely, the illumination lightemerging from a point on the pupil plane 15 is converted into anapproximately parallel beam to illuminate the reticle R while beingincident at a predetermined incidence angle and incidence direction. Theincidence angle and incidence direction are determined according to theposition of the beam on the pupil plane 15.

The path bending mirrors 7, 19 are not always indispensable in terms ofoptical performance, but if the illumination optical system ILS isarranged on a line the total height of the exposure apparatus (theheight in the Z-direction) will increase; therefore, they are arrangedat appropriate positions in the illumination optical system ILS for thepurpose of space saving. The optical axis of illumination system AX1coincides with the optical axis of illumination system AX2 throughreflection on the mirror 7, and the optical axis of illumination systemAX2 further coincides with the optical axis of illumination system AX3through reflection on the mirror 19.

A first example of the first and second birefringent members 12, 13 inFIG. 1 will be described below with reference to FIGS. 2 to 5.

The first birefringent member 12 is a member of disk shape made of abirefringent material such as a uniaxial crystal, and the optical axisthereof is in its in-plane direction (direction parallel to the planenormal to the optical axis of illumination system AX2). The size(diameter) in the in-plane direction of the first birefringent member 12is larger than the beam size of the illumination light IL at theposition where the birefringent member 12 is located.

FIG. 2A is a view of the birefringent member 12 in FIG. 1 viewed to the+Y direction and along the optical axis of illumination system AX2 andin the birefringent member 12, as shown in FIG. 2A, the fast axis nf,which is an axial direction to minimize the refractive index forlinearly polarized light with the polarization direction parallelthereto, is directed in a direction rotated by 45° from each coordinateaxis (X-axis and Z-axis) in the XZ coordinate system with the samecoordinate axes as in FIG. 1. Furthermore, the slow axis ns, which is anaxial direction to maximize the refractive index for linearly polarizedlight with the polarization direction parallel thereto, is naturallyorthogonal to the fast axis nf and is also directed in a directionrotated by 45° from both of the X-axis and Z-axis.

The thickness of the first birefringent member 12 is not uniform in aplane parallel to the plane of FIG. 2A, and varies according toX-coordinates (positions in the X-direction). FIG. 2B is a sectionalview of the birefringent member 12 along line AA′ in FIG. 2A and, asshown in FIG. 2B, the birefringent member 12 has such a shape that it isthin at the center (the optical axis of illumination system) and thickin the marginal region in the X-direction. On the other hand, thethickness of the first birefringent member 12 is uniform in theZ-direction in FIG. 2A and thus the birefringent member 12 is of a shapelike a negative cylinder lens as a whole.

A beam passing through such a birefringent member generally has a pathdifference (polarization phase difference) between a linear polarizationcomponent with the polarization direction (i.e., “vibrating direction ofthe electric field of light,” which will also apply to the descriptionhereinafter) coinciding with the direction of the fast axis nf, and alinear polarization component with the polarization direction coincidingwith the direction of the slow axis ns. The refractive index of thebirefringent member is low for linearly polarized light parallel to thefast axis nf, so that the traveling speed of the same polarized light ishigh. On the other hand, the refractive index of the birefringent memberis high for linearly polarized light parallel to the slow axis ns, sothat the traveling speed of the same polarized light is low. Therefore,there appears a path difference (polarization phase difference) betweenthe two polarized beams. Therefore, the first birefringent member 12functions as a first nonuniform wavelength plate in which thepolarization phase difference given to transmitted light differsaccording to locations.

Incidentally, if the thickness of the first birefringent member 12 isoptimized to make the path difference due to the birefringent member 12equal to an integer multiple of a wavelength, the phases of the twobeams cannot be substantially discriminated from each other, and a statesubstantially having no optical path difference can be realized. In thepresent example, the thickness T1 of the center part of the birefringentmember 12 is set to such thickness. In the description hereinafter, asshown in FIG. 2B, the origin of the X-axis (X=0) is defined at thecenter of the birefringent member 12 (optical axis of illuminationsystem).

On the other hand, the shape of the birefringent member 12 is so setthat the polarization phase difference becomes 0.5 (in the unit of thewavelength of the illumination light) at positions of ±1 apart in theX-direction from the center of the first birefringent member 12 (where 1represents a reference length and is located inside the outer diameterof the first birefringent member 12). For realizing such shape, thepresent example defines the thickness TA of the birefringent member 12as the thickness represented by the following function, for the positionX in the X-direction.

TA=T1+α(1.7X ⁴−0.7X ²)  (1)

In the above equation, α is a proportionality coefficient, and the valueof a varies depending upon the aforementioned index difference betweenthe fast axis and the slow axis of the birefringent material used, orthe like as the thickness T1 of the center part does.

When crystalline quartz being a uniaxial crystal is used as thebirefringent material making the first birefringent member 12, therefractive indices of crystalline quartz are as follows: the refractiveindex of 1.6638 for an ordinary ray and the refractive index of 1.6774for an extraordinary ray in the ArF excimer laser light with thewavelength of 193 nm. Therefore, the fast axis is the polarizationdirection of the ordinary ray and the slow axis the polarizationdirection of the extraordinary ray.

The wavelengths of the ordinary ray and extraordinary ray in crystallinequartz are obtained by diving the wavelength (193 nm) in vacuum by therespective refractive indices, and are thus 116.001 nm and 115.056 nm,respectively. Therefore, a path difference of 0.945 nm is made betweenthe two rays with every travel through one wavelength in crystallinequartz. Accordingly, after travel through 122.7 (=116.001/0.945)wavelengths, the path difference of about one wavelength is createdbetween the two rays. However, the path difference of just onewavelength or an integral multiple of the wavelength is equivalent tosubstantially no path difference between the two rays. The thickness ofcrystalline quartz corresponding to the 122.7 wavelengths is obtained bycalculation of 122.7 193/1.6638, and is equivalent to 14239 nm, i.e.,14.239 μm. Similarly, for making a path difference of a half wavelengthbetween the ordinary ray and the extraordinary ray, the thickness ofcrystalline quartz can be set to a half of the above thickness, i.e.,7.12 μm.

This confirms that when the first birefringent member 12 being the firstnonuniform wavelength plate is made of crystalline quartz, the thicknessT1 of the center part in Eq (1) above is set to an integer multiple of14.239 μm and the thickness at the reference position (X=1) near themarginal region is set to a thickness 7.12 μm larger than it, i.e., theaforementioned proportionality coefficient α can be set to 7.12 μm.

At this time, the polarization phase difference ΔP1 made by the firstbirefringent member 12 is represented as follows as a function ofposition X in the X-direction.

ΔP1=0.5(1.7X ⁴−0.7X ²)  (2)

The thickness of the first birefringent member 12 is a spacing betweenits entrance surface 12 a and exit surface 12 b, and each of shapes ofthe entrance surface 12 a and exit surface 12 b may be arbitrary as longas they satisfy the aforementioned relation between thickness andX-directional position for formation of the phase difference. From theviewpoint of processing of surface shape, however, processing becomeseasier if either surface is a plane, and it is thus desirable to make,for example, the exit surface 12 b as a plane in practice, as shown inFIG. 2B. In this case, where the value of the thickness TA on the exitsurface 12 b is 0, values of thickness TA of the entrance surface 12 aare equal to those of TA determined by Eq (1). It is a matter of coursethat the entrance surface 12 a is constructed as a plane.

FIG. 4A is a diagram showing the relation between polarization phasedifference ΔP1 (in the unit of the wavelength of illumination light) andposition X represented by Eq (2). FIG. 5 is a drawing showingpolarization states of the illumination light emerging from the firstbirefringent member 12 and in FIG. 5 a polarization state ofillumination light distributed at each position on the XZ coordinates isindicated by a line segment, a circle, or an ellipse with the center ateach position. The origins of the X-axis and Z-axis (X=0 and Z=0) inFIG. 5 are set at the center of the birefringent member 12, and thescales in the X-direction and in the Z-direction are so set that thepositions of X=±1 and Z=±1 (both of which are positions the referencelength apart from the origin X=0, Z=0) are located at the four cornersin FIG. 5.

At a position represented by each line segment among the positionsidentified by the respective XZ coordinates in FIG. 5, the illuminationlight is in a polarization state consisting primarily of linearpolarization and a direction of the line segment indicates apolarization direction thereof. At a position represented by eachellipse, the illumination light is in a polarization state consistingprimarily of elliptic polarization and a direction of the major axis ofthe ellipse indicates a direction in which the linear polarizationcomponent in the elliptic polarization is maximum. At a positionrepresented by each circle, the illumination light is in a polarizationstate consisting primarily of circular polarization.

At the positions ±1 apart in the X-direction from the center, as shownin FIG. 4(A), the first birefringent member 12 acts as a so-called halfwavelength plate. Here the illumination light IL emitted from theexposure light source 1 in FIG. 1 consists primarily of the linearlypolarized light polarized in the X-direction as described previously,and the half wavelength plate has the fast axis nf and slow axis nsrotated 45° relative to the X-direction being the polarization directionof the incident light (or of the illumination light). Therefore, asshown in FIG. 5, the polarization state of the illumination lightpassing near the positions ±1 (reference length) apart in theX-direction from the center in the first birefringent member 12 isconverted into the polarization state consisting primarily of linearpolarization in the Z-direction by the action of the half wavelengthplate.

For the illumination light passing near the positions ±0.6 apart in theX-direction from the center in the first birefringent member 12, asshown in FIG. 4A, the polarization phase difference ΔP1 is 0.25 and thefirst birefringent member 12 acts as a so-called quarter wavelengthplate. For this reason, the illumination light passing this part isconverted into a polarization state consisting primarily of circularpolarization.

On the other hand, there is no path difference between the linearpolarization in the direction of the fast axis nf and the linearpolarization in the direction of the slow axis ns in a beam passing thecenter in the X-direction, and thus no conversion occurs for thepolarization state of transmitted light. Therefore, a beam incident atthe center in the X-direction into the birefringent member 12 emergesfrom the birefringent member 12 while maintaining the state consistingprimarily of the linear polarization state in the X-direction. Thenbeams passing at positions except for the above positions of X=0, ±0.6,and ±1 pass through the first birefringent member 12, in polarizationstates consisting primarily of elliptic polarization in different shapesaccording to the positions. The polarization states are as shown in FIG.5.

In FIG. 1, the illumination light IL in the different polarizationstates according to the passing locations through the first birefringentmember 12 is incident to the second birefringent member 13. The secondbirefringent member 13 is also a member of disk shape made of abirefringent material.

FIG. 3A is a view of the second birefringent member 13 in FIG. 1, viewedto the +Y direction and along the optical axis of illumination systemAX2, and, as shown in FIG. 3(A), the fast axis of the secondbirefringent member 13 is set in parallel with the Z-axis of the XZcoordinate system with the same coordinate axes as those in FIG. 1 andthe slow axis ns is set in parallel with the X-axis, different from theaforementioned first birefringent member 12. Concerning the secondbirefringent member 13, the size (diameter) in the in-plane directionthereof is larger than the beam size of the illumination light IL at theposition where the second birefringent member 13 is located.

The thickness of the second birefringent member 13 is not uniform,either, and the thickness also varies according to positions in thedirection of the function Z=X in the XZ coordinate system in FIG. 3(A),i.e., in the direction of line BB′ in FIG. 3A (which will be referred tohereinafter as “XZ direction”). FIG. 3(B) is a sectional view of thesecond birefringent member 13 along line BB′ in FIG. 3A, and, as shownin FIG. 3B, the birefringent member 13 has such a shape that it is thinat the left end (near B) and thick at the right end (near B′). On theother hand, the thickness of the second birefringent member 13 isuniform in the direction orthogonal to the XZ direction. Therefore, thesecond birefringent member 13 also functions as a second nonuniformwavelength plate in which the polarization phase difference given to thetransmitted light differs according to locations.

In the present example the thickness TB of the second birefringentmember 13 is represented by the following function, for the position XZin the XZ direction. As shown in FIG. 3(B), the origin in the XZdirection (XZ=0) is defined at the center of the birefringent member 13(the optical axis of illumination system) and the thickness at thecenter is defined by T2.

TB=T2+β(2.5XZ ⁵−1.5XZ ³)  (3)

In this equation, β is a proportionality coefficient and the value of βdiffers depending upon the aforementioned index difference between thefast axis and the slow axis of the birefringent material used, or thelike as the thickness T2 of the center part does. Here the thickness T2of the center part is so set that the polarization phase difference ΔP2of the second birefringent member 13 is 0.25 (in the unit of thewavelength of the illumination light), i.e., that the center partfunctions as a quarter wavelength plate.

The birefringent member 13 is also so set that the polarization phasedifferences ΔP2 at the positions +1 (reference length) and −1 apart inthe XZ direction are +0.75 and −0.25, respectively. This means thatdifferences of +0.5 and −0.5, respectively, are made between thepolarization phase differences at the positions of interest and at thecenter.

Namely, in the second birefringent member 13 of the present example thethickness thereof is so set that the polarization phase difference ΔP2is represented by the following equation.

ΔP2=0.25+0.5(2.5XZ ⁵−1.5XZ ³)  (4)

In a case where the second birefringent member 13 is also made ofcrystalline quartz as in the case of the aforementioned example, thethickness T2 of the center part can be set to an (integer+¼) multiple of14.239 μm and the proportionality coefficient β to 7.12 μm. FIG. 4(B) isa drawing showing the relation between polarization phase difference ΔP2and position XZ of Eq (4).

In FIG. 1, the second birefringent member 13 again converts theillumination light in the different polarization states according to thepassing locations through the first birefringent member 12, intopolarization states according to locations. FIG. 4C shows thepolarization states of the illumination light IL emerging from thesecond birefringent member 13.

FIG. 4C is illustrated in the same manner as the aforementionedillustration method in FIG. 5, and, in FIG. 4C, a polarization state ofillumination light distributed at each position on XZ coordinates isindicated by a line segment (linear polarization) or an ellipse(elliptic polarization) with the center at each position. The origins ofthe X-axis and Z-axis in FIG. 4C (X=0 and Z=0) are also set at thecenter of the birefringent member 13.

In the present embodiment, as shown in FIG. 1, the first birefringentmember 12 and the second birefringent member 13 are located immediatelybefore the fly's eye lens 14 and the exit-side surface of the fly's eyelens 14 is located near the pupil plane 15 in the illumination opticalsystem ILS. For this reason, the first birefringent member 12 and thesecond birefringent member 13 are located at positions substantiallyequivalent to the pupil plane 15 in the illumination optical system ILS.

Therefore, the illumination light IL passing through the firstbirefringent member 12 and the second birefringent member 13 is incidentat incidence angles and incidence directions determined according to thelocations, into the reticle R. Namely, a beam distributed on the origin(the position of X=0 and Z=0) in FIG. 4C is incident normally to thereticle R, and a beam distributed at a position a predetermined distanceapart from the origin is incident at an incidence angle proportionalapproximately to this distance, to the reticle R. The incidencedirection of the beam is a direction equal to an azimuth of that pointfrom the origin.

Exterior circle C1 and interior circle C2 shown in FIG. 4C and FIG. 5are boundaries of a distribution of the illumination light for formingpredetermined annular illumination on the reticle R. The radii of therespective circles C1, C2 are determined as follows: the radius of theexterior circle C1 is 1.15 and the radius of the interior circle C20.85, where the unit is the reference length used in determining thethickness shapes (thickness profiles) of the first birefringent member12 and the second birefringent member 13. Namely, an annular ratio ofthe annular illumination (radius of interior circle/radius of exteriorcircle) is assumed to be 0.74. This is based on the assumption ofso-called “¾ annular illumination (interior radius:exterior radius 3:4)”used in general, but it is a matter of course that the condition for theannular illumination to which the present invention is to be applied isnot limited to this.

As apparent from FIG. 4C, the illumination light emerging from thesecond birefringent member 13 is in polarization states consistingprimarily of linear polarization with the polarization direction alongthe circumferential direction of a specific annular region 36, in thespecific annular region 36 which is an annular region between theexterior circle C1 and the interior circle C2.

When comparing FIG. 4C with FIG. 5, the polarization states of theillumination light on the X-axis and on the Z-axis are almost equal.However, the polarization states at positions approximately 45° apartfrom each axis about the origin (at the upper right, upper left, lowerleft, and lower right positions in FIG. 4C and FIG. 5) are almostcircular polarization in FIG. 5, but are linear polarization along thecircumferential direction of the specific annular region in FIG. 4C.This arises from the action of the second birefringent member 13; thesecond birefringent member 13 functions as a quarter wavelength plate inthe upper left and lower right regions in FIG. 4C and functions as a −¼wavelength plate and as a ¾ wavelength plate equivalent thereto in thelower left and the upper right regions, respectively.

In the practical exposure apparatus, the actual radius of the exteriorcircle C1 of the specific annular region 36 is determined by thenumerical aperture (NA) on the reticle R side of the projection opticalsystem 25 in FIG. 1, the focal length of the optical system consistingof the relay lens 16 and condenser lenses 18, 20 in the illuminationoptical system ILS, and the value of coherence factor (illumination σ)to be set, and the radius of the interior circle C2 is a valuedetermined further by the annular ratio to be set. It is needless tomention that for this condition for annular illumination, the thicknessshapes of the first birefringent member 12 and second birefringentmember 13 are determined so that the polarization directions of theillumination light distributed in the specific annular region 36 arecoincident with the circumferential direction of the annular region atthe respective positions.

To determine the thickness shapes of the first birefringent member 12and the second birefringent member 13 means that the shapes areproportionally enlarged or reduced in the XZ plane and unevennessamounts thereof are kept unchanged in the Y-direction (travelingdirection of light).

In the first example of the first and second birefringent members 12,13, as described above, the polarization directions of the illuminationlight distributed in the specific annular region can be made coincidentwith the circumferential direction of the annular region at eachposition, with no light quantity loss of the illumination beam, by thefirst and second nonuniform wavelength plates. In this case, theillumination light incident through the specific annular region 36 ontothe reticle R among the illumination light, i.e., the specificillumination beam incident in the specific incidence angle range to thereticle R is light in the polarization state consisting primarily ofS-polarization whose polarization direction lies along the directionnormal to the entrance plane. This improves the contrast, resolution,depth of focus, etc. of the transferred image, depending upon theperiodicity of the pattern to be transferred, in some cases (the detailsof which will be described later).

Next, the second example of the first and second birefringent members12, 13 in the illumination optical system ILS in FIG. 1 will bedescribed with reference to FIG. 6.

In the present example the configurations of the first birefringentmember 12 and the second birefringent member 13 are basically the sameas those in the aforementioned first example. Namely, the firstbirefringent member 12 has the direction of the fast axis and thethickness shape as shown in FIG. 2A and FIG. 2B and the secondbirefringent member 13 has the direction of the fast axis and thethickness shape as shown in FIG. 3A and FIG. 3B. In the present example,however, the function forms for the thicknesses of the two birefringentmembers 12, 13 are different.

FIG. 6A, corresponding to FIG. 4A, shows a characteristic ofpolarization phase difference ΔP1 by the first birefringent member 12versus X-directional position in the second example. The polarizationphase difference ΔP1 in FIG. 6A is represented by the following functionincluding a trigonometric function about position X.

ΔP1=0.265{1−cos(πX ²)}  (5)

This polarization phase difference ΔP1 can be realized by expressing thethickness TA of the first birefringent member 12 by the followingfunction for the X-directional position X.

TA=T1+γ{1−cos(πX ²)}  (6)

In this equation, γ represents a proportionality coefficient. In a casewhere the first birefringent member 12 is made of crystalline quartz, asin the first embodiment, the thickness T1 at the center can be set to aninteger multiple of 14.239 μm and the proportionality coefficient γ to3.77 μm. The value of 3.77 μm is obtained by multiplying the thicknessof crystalline quartz for giving the polarization phase difference ofone wavelength, 14.239 μm, by the coefficient of 0.265 in Eq (5) above.

FIG. 6B shows a characteristic of polarization phase difference ΔP2 bythe second birefringent member 13 versus XZ-directional position in thesecond example. The polarization phase difference ΔP2 in FIG. 6(B) canbe represented by the following function including a trigonometricfunction about position XZ.

ΔP2=0.25+0.5 sin(0.5πXZ ³)  (7)

The polarization phase difference ΔP2 can be realized by expressing thethickness TB of the second birefringent member 13 by the followingfunction for the position XZ in the XZ direction.

TB=T2+δ sin(0.5πXZ ³)  (8)

In this equation δ is a proportionality coefficient. When the secondbirefringent member 13 is made of crystalline quartz, the thickness T2at the center can be set to an (integer+¼) multiple of 14.239 μm, andthe proportionality coefficient δ to 7.12 μm.

In the present example the first birefringent member 12 and the secondbirefringent member 13 also function as first and second nonuniformwavelength plates, respectively, in which the polarization phasedifference given to the transmitted light differs according tolocations. Then the linearly polarized light incident in a polarizedstate in the X-direction into the first birefringent member 12 isconverted into the polarization distribution shown in FIG. 6C to emergefrom the second birefringent member 13.

As seen from comparison between FIG. 6C and FIG. 4C, the firstbirefringent member 12 and second birefringent member 13 of the presentsecond example can make the polarization states of illumination lightdistributed in the specific annular region 36 between the exteriorcircle C1 and the interior circle C2, closer to linear polarizationparallel to the circumferential direction of the annular region 36 thanthose in the first example. The reason for it is that the firstbirefringent member 12 and second birefringent member 13 of the presentsecond example adopt the thickness shapes (i.e., surface shapes)determined by the high-order functions of trigonometric functions andthus they enable higher-accuracy polarization control.

However, since the first birefringent member 12 and second birefringentmember 13 in the first example are represented by the functions of atmost order 5, they offer the advantage that processing is easy andproduction cost is low, though they are slightly inferior in thepolarization control performance.

In order to further reduce the production cost of the first and secondbirefringent members 12, 13, it is also possible, for example, to adopta configuration wherein the surface shape of the first birefringentmember 12 is a cylindrical surface (surface of a circular cross sectionin the X-direction) and wherein the surface shape of the secondbirefringent member 13 is a tapered surface (inclined plane). Thepolarization control performance in this case is worse than in the firstembodiment, but satisfactory effect can be achieved thereby dependingupon use of the projection exposure apparatus. Therefore, it can realizea high-performance exposure apparatus while achieving the reduction ofproduction cost.

The configuration wherein the surface shape of the second birefringentmember 13 is the tapered surface means that the polarization phasedifference of a beam passing through the second birefringent member 13is defined in a linear form (linear function) according to locations inthe plane of the second birefringent member 13.

Incidentally, the shapes of the first birefringent member 12 and thesecond birefringent member 13 in FIG. 1 are not limited to the shapesshown in the above first and second examples, but may be any shapes thatcan make the polarization state of transmitted light in the specificannular region coincide with the circumferential direction in each part.

For example, the shapes of the first birefringent member 12 and secondbirefringent member 13 may be stepwise shapes with stepped shape changesat predetermined positions, instead of the shapes represented by theaforementioned continuous and differentiable continuous functions. Suchstepwise shapes can be formed suitably by etching, instead of mechanicalor mechanochemical polishing.

In order to implement the polarization states as described above, in thecase where the illumination light is such that the polarization state ofthe beam incident to the first birefringent member 12 is the singlepolarization state consisting primarily of linear polarization, thefirst birefringent member 12 is preferably one that gives thepolarization phase difference with 2-fold rotation symmetry around theoptical axis of illumination system AX2. It is a matter of course thatthis embraces the nonuniform wavelength plate having the thickness of aneven function in the X-direction and the constant thickness in theY-direction, as shown in the above-described first and second examples.

The second birefringent member 13 is desirably the nonuniform wavelengthplate that gives the polarization phase difference with 1-fold rotationsymmetry about the optical axis of the illumination system AX2. The1-fold rotation symmetry refers to a state in which the distribution ofpolarization phase differences is approximately symmetric with respectto one axis out of two axes orthogonal to the optical axis ofillumination system AX2 and approximately antisymmetric with respect tothe other axis. The antisymmetry generally refers to a function thatprovides equal absolute values but opposite signs with inversion of acoordinate axis, but the antisymmetry herein also embraces functionsobtained by adding an offset of a constant to general antisymmetricfunctions. It is needless to mention that this encompasses thenonuniform wavelength plate having the thickness determined by an oddfunction with an offset in the XZ-direction and the constant thicknessin the direction orthogonal thereto, as shown in the above-describedfirst and second examples.

In the present embodiment, particularly, it is important to set theillumination light distributed in the aforementioned specific annularregion to the predetermined polarization state; therefore, it is obviousas to the shapes of the first birefringent member 12 and the secondbirefringent member 13 that no particular problem will arise even if theshapes in the portions not corresponding to the foregoing specificannular region do not satisfy the above conditions.

The number of first birefringent member 12 and second birefringentmember 13, and the directions of the fast axes thereof are not limitedto those described in the above first and second examples, either.Specifically, three or more birefringent members may be arranged inseries along the traveling direction of the illumination light (alongthe optical axis of illumination system AX2), and the rotationalrelation around the optical axis AX2 between the directions of the fastaxes is not limited to 45°, either. In the case where three or morebirefringent members are arranged in series along the travelingdirection of the illumination light, a potential configuration is suchthat the direction of the fast axis of at least one birefringent memberout of the plurality of birefringent members is different from thedirections of the fast axes of the other birefringent members, in orderto convert the polarization state of the illumination light into linearpolarization nearly parallel to the circumferential direction in atleast a partial region of the aforementioned specific annular regionand, desirably, in the almost entire circumferential region.

Similarly, the materials of the birefringent members 12, 13 and othersare not limited to crystalline quartz described above, either, but otherbirefringent materials are also applicable. It is also possible to usethe intrinsic birefringence of fluorite to form the birefringentmembers. A material originally having no birefringence, e.g., syntheticquartz, comes to have the birefringent property when subjected to stressor the like. It can also be used for the birefringent members 12, 13 andothers.

Furthermore, the birefringent members 12, 13 can also be made using acomposite material obtained by bonding a material with birefringenceonto a transparent substrate without birefringence. In this case, theaforementioned thicknesses are, of course, thicknesses of the materialwith birefringence. The bonding herein may be implemented not only bymechanical joining such as adhesion or press, but also by a method offorming a thin film with birefringence on the transparent substrate bymeans such as vapor deposition or the like. The thickness shapes andothers of the first birefringent member 12 and second birefringentmember 13 described in the above first and second examples varydepending upon the magnitude of birefringence of the material used, but,even in cases where materials except for crystalline quartz are used,the aforementioned shape determining method can also be applied and theshapes are determined thereby, of course.

The advantage of the illumination light in the annular illumination asdescribed above, in which the polarization state of the illuminationlight distributed in the annular region is coincident with thecircumferential direction of the annular region, will be describedbriefly with reference to FIGS. 7 and 8.

FIG. 7A shows an example of fare periodic pattern PX formed on thereticle R in FIG. 1. The periodic pattern PX is a pattern withperiodicity in the X-direction in the same XYZ coordinate system as inFIG. 1, and the pitch PT thereof is 140 nm as a converted value in termsof the scale on the wafer W in consideration of the projectionmagnification of the projection optical system 25 in FIG. 1. FIG. 7Bshows a distribution of diffracted light formed in the pupil plane 26(cf. FIG. 1) of the projection optical system 25 with the wafer-sidenumerical aperture (NA) of 0.90 when this pattern is illuminated byannular illumination with the coherence factor (illumination δ) of 0.9and the annular ratio of 0.74, using the illumination light having thewavelength of 193 nm.

FIG. 7C is a drawing showing the condition for annular illumination forilluminating the pattern PX, and the pattern PX is illuminated with theillumination light from the annular region IL0 satisfying the abovecondition for annular illumination, in the pupil plane 15 of theillumination optical system ILS in FIG. 1. The whole of 0-orderdiffracted light D0 in FIG. 7B from the periodic pattern PX isdistributed in the pupil plane 26 and passes through the projectionoptical system 25 to reach the wafer W, but the 1-order diffracted lightD1R and D1L can be transmitted only in part through the pupil plane 26and the projection optical system 25. An image of the pattern PX on thereticle R is formed as an interference fringe pattern between the0-order diffracted light D0 and the 1-order diffracted light D1R, D1L,on the wafer W, but an interference fringe pattern is formed only by apair of 0-order diffracted light and 1-order diffracted light generatedfrom the illumination light emitted from the same position on the pupilplane 15 of the illumination optical system LLS.

The 1-order diffracted light D1L located at the left end of the pupilplane 26 in FIG. 7B is to be paired with the part of the 0-orderdiffracted light D0 located at the right end, and those diffracted lightbeams originate in the illumination light from the right-end partialregion ILR in the annular region. IL0 in FIG. 7C. On the other hand, the1-order diffracted light D1R located at the right end of the pupil plane26 in FIG. 7B is to be paired with the part of the 0-order diffractedlight D0 located at the left end, and those diffracted light beamsoriginate in the illumination light from the left-end partial region ILLin the annular region IL0 in FIG. 7C.

Namely, on the occasion of exposure of the pattern PX with the finepitch in the X-direction, beams contributing to imaging of the patternPX among the illumination light emitted from the annular region IL0 onthe pupil plane 15 of the illumination optical system ILS are limited tothose in the partial region ILR and partial region ILL, and theillumination light emitted from the other regions in the annular regionIL0 is illumination light not contributing to imaging of the pattern PX.

Incidentally, aforementioned Non-patent Document 1 (Thimothy A. Brunner,et al.: “High NA Lithographic imaging at Brewster's angle,” SPIE Vol.4691, pp. 1-24 (2002) and others report that on the occasion of exposureof a pattern with periodicity in the X-direction and with thelongitudinal direction along the Y-direction like the pattern PX, thecontrast of its projected image is improved by illumination with linearpolarization having the polarization direction along the Y-direction onthe reticle R.

Therefore, it is effective in improvement in the contrast of theprojected image of the pattern PX and in improvement in the resolutionand depth of focus in turn, to convert the illumination lightdistributed in the partial region ILR and in the partial region ILL inFIG. 7(C), into linearly polarized light polarized in the PR directionand the PL direction (corresponding to the Y-direction on the reticle Rin consideration of the action of mirror 19 in FIG. 1) parallel to theZ-direction in FIG. 7C.

When the reticle pattern is a periodic pattern with a fine pitch in theY-direction resulting from 90° rotation of the pattern PX of FIG. 7A,the diffracted light distribution is also one rotated 90° from thatshown in FIG. 7B. As a result, the partial regions through which theillumination light contributing to image formation of the periodicpattern passes are also located at the positions resulting from 90°rotation of the partial region ILR and partial region ILL shown in FIG.7C (i.e., at the upper end and at the lower end in FIG. 7C) and thepreferred polarization state is linear polarization with thepolarization direction coincident with the X-direction. From the above,it is effective to use the illumination light in the polarization stateas shown in FIG. 8, on the occasion of exposure of the reticle Rincluding a pattern PX with fine periodicity in the X-direction and apattern PY with fine periodicity in the Y-direction.

FIG. 8A is a perspective view showing the simplified relation betweenthe pupil plane 15 of the illumination optical system ILS and thereticle R in FIG. 1, without illustration of the relay lens 16,condenser lenses 18, 20, and others in FIG. 1. As described above, theillumination light distributed in the annular region IL0 in FIG. 8A isdesirably linear polarization in the Y-direction (the depth direction inthe plane of FIG. 8A) at the ends ILL, ILR in the X-direction, in orderto improve the imaging performance of the pattern PX with periodicity inthe X-direction, and it is desirably linear polarization in theX-direction at the ends ILU, ILD in the Y-direction, in order to improvethe imaging performance of the pattern PY with periodicity in theY-direction. Namely, it is desirable to use linear polarization with thepolarization direction approximately coincident with the circumferentialdirection of the annular region IL0.

Furthermore, in a case where the reticle R includes not only thepatterns in the X-direction and in the Y-direction but also patterns inintermediate directions (45° and 135° directions), it is desirable touse linear polarization with the polarization direction perfectlycoincident with the circumferential direction of the annular region,taking orientations of these patterns into consideration as well.

In passing, the above-described polarization states do not alwaysrealize effective polarization states for the patterns perpendicular tothe patterns with orientations suitable for the polarization states ofthe respective portions in the annular region IL0. For example, theillumination light polarized in the X-direction from the partial regionILU is not in a preferred polarization state for imaging of the patternPX with the periodicity in the X-direction and with the longitudinaldirection along the Y-direction. As apparent from FIG. 7C showing thelight sources contributing to the imaging of the pattern with the finepitch in the X-direction, however, the partial region ILU correspondingto the upper end of the annular region IL0 in FIG. 7C is primarily thelight source not contributing to the imaging of the pattern with thefine pitch in the X-direction at all and, therefore, no matter whichpolarization state is taken by the partial region ILU, the polarizationstate thereof will never cause degradation of the imagingcharacteristics.

As shown in FIG. 8A, the linear polarization almost coincident with thecircumferential direction of the annular region IL0 on the pupil plane15 of the illumination optical system ILS is incident as so-calledS-polarization to the reticle R. The S-polarization refers to linearpolarization with the polarization direction perpendicular to a plane ofincidence in which a beam is incident to an object (which is a planeincluding a normal to the object, and the beam). Namely, theillumination light ILL1 from the partial region ILL consisting oflinearly polarized light in the direction coincident with thecircumferential direction of the annular region IL0 is incident asS-polarization with the polarization direction EF1 normal to the planeof incidence (the plane of FIG. 8B), as shown in FIG. 8B, to the reticleR. The illumination light ILD1 on the similar partial region ILD is alsoincident as S-polarization with the polarization direction EF2 normal tothe plane of incidence (the plane of FIG. 8C), as shown in FIG. 8C, tothe reticle R.

Naturally, the illumination light from the partial regions ILR, ILU atthe positions symmetric with the foregoing partial regions ILL, ILD withrespect to the optical axis AX41 of the illumination optical system isalso incident as S-polarization to the reticle R by virtue of symmetry,because each illumination light on the partial region ILR, ILU has thepolarization direction coincident with the circumferential direction ofthe annular region IL0. It is the general property of the annularillumination that angles of incidence of the illumination lightdistributed on the annular region IL0, to the reticle R are in apredetermined angular region with the center at an angle φ from theoptical axis AX41 of the illumination optical system (i.e., a normal tothe reticle R). A beam incident at the angles of incidence to thereticle R will be referred to hereinafter as “specific illuminationbeam.” The angle φ and angular range can be determined based on thewavelength of the illumination light, the pitch of the pattern to betransferred, on the reticle R, and so on.

Incidentally, the foregoing first and second birefringent members 12, 13convert the polarization state of the illumination light distributed inthe specific annular region between the predetermined outside radius(exterior circle C1) and inside radius (interior circle C2) determinedfrom the shapes peculiar to the members, into the polarization stateconsisting primarily of linear polarization parallel to thecircumferential direction of the specific annular region, and it is noteasy to change the radii (C2, C1).

In the case where there arises a need for changing the desired annularregion, for example, on the basis of the pitch of the pattern to betransferred, on the reticle R, as described above, a desirableconfiguration is such that a plurality of conical prisms 41, 42 of azoom type are disposed between the first and second birefringent members12, 13 and the optical integrator such as the fly's eye lens 14 in FIG.1, as shown in FIG. 9, to make the radii of the foregoing specificannular region variable. In FIG. 9, the plurality of conical prisms ofthe zoom type are a concave conical prism 41 with a concave conicalsurface 41 b and a convex conical prism 42 with a convex conical surface42 a, which are arranged with a spacing DD variable between them andalong the optical axis of illumination system AX2.

In this case, the illumination light distributed in the specific annularregion with the center at an average radius RI after passage through thefirst and second birefringent members 12, 13 is enlarged to a radius ROon the entrance plane of the fly's eye lens 14 and on the pupil plane 15of the illumination optical system being the exit plane of the fly's eyelens 14, by the zoom type conical prisms 41, 42. This radius RO can beenlarged by increasing the spacing DD between the two conical prisms 41,42 and can be reduced by decreasing the spacing DD.

This makes it feasible to form the specific annular region as adistribution of the illumination light consisting of linear polarizationparallel to the circumferential direction, with arbitrary radii on thepupil plane 15 of the illumination optical system, and to change theillumination condition for annular illumination in accordance with thepattern on the reticle R to be transferred.

It is a matter of course that a zoom optical system can be used insteadof the foregoing zoom type conical prisms 41, 42.

Incidentally, the above embodiment was described on the premise that theillumination light quantity distribution formed on the pupil plane 15 ofthe illumination optical system ILS in FIG. 1 is the annular region,i.e., that it is applied to the annular illumination, but theillumination condition that can be realized by the projection exposureapparatus of FIG. 1 is not always limited to the annular illumination.Namely, since the birefringent members 12, 13 of FIG. 1 and the zoomtype conical prisms 41, 42 of FIG. 9 are configured to set thepolarization state of the illumination light distributed in the specificannular region in the pupil plane 15 of the illumination optical systemto the desired polarization state, it is needless to mention that evenin the case where the distribution of the illumination light is furtherlimited to within a specific partial region in the specific annularregion, i.e., where the distribution of the illumination light islimited, for example, to the partial regions ILL, ILR in FIG. 7C, theycan convert the illumination light distributed in the partial regions,into illumination light consisting primarily of linear polarization withthe polarization direction parallel to the circumferential direction ofthe specific annular region.

In order to condense the illumination light only into the furtherspecific regions in the specific annular region in this manner, thediffractive optical element 9 a in FIG. 1 is replaced with such adiffractive optical member that the diffracted light (illuminationlight) generated from the other diffractive optical element isconcentrated in the further specific discrete regions in the specificannular region on the first birefringent member 12 and on the secondbirefringent member 13. The locations where the illumination light iscondensed are, for example, two locations of the partial regions ILL,ILR in FIG. 7C, but are not limited to this example. The illuminationlight may be condensed at arbitrary locations in the specific annularregion, and the number of locations may be four. The locations may beselected according to the shape of the pattern as an exposed object onthe reticle R.

In the case where the illumination light is condensed in the furtherspecific regions in the specific annular region as described above, itis also possible to use, instead of the zoom type conical prisms 41, 42,an optical member group as a combination of a convex polyhedron prismand a concave polyhedron prism of pyramid shape or the like with avariable spacing similarly.

Since the illumination light distributed in the regions except for thesespecific regions is not suitable for exposure of the pattern as theexposed object, the light quantity distribution thereof is preferablysubstantially 0 in certain cases. On the other hand, manufacturing erroror the like of the diffractive optical element 9 a and others couldproduce diffracted light (hereinafter referred to as “error light”) indirections except for the desired directions from the diffractiveoptical element 9 a and others and cause the illumination light to bedistributed in the regions except for the above partial regions. It isthus also possible, for example, to adopt a configuration wherein a stopis disposed on the entrance surface side or on the exit surface side ofthe fly's eye lens 14 in FIG. 1 to block the error light. This makes theillumination light quantity distributions in the plurality of specificregions perfectly discrete. However, there are cases where anotherpattern exists except for the pattern as the exposed object on thereticle R and where the error light is effective to imaging of thepattern except for the object. Therefore, the illumination lightquantity distribution in the region except for the specific regions doesnot always have to be 0 in such cases.

Incidentally, with attention to incidence of the illumination light tothe reticle R, the limitation of the distribution of the illuminationlight quantity on the pupil plane 15 to within the further specificregions in the specific annular region results in further limiting theincidence directions thereof to only the aforementioned plurality ofsubstantially discrete directions, in addition to the restriction on therange of incidence angles by the annular illumination. Naturally, in thecase where the present invention is applied to the annular illumination,it is also possible to adopt the configuration wherein a stop isdisposed on the entrance surface side or on the exit surface side of thefly's eye lens 14 to block the error light distributed in the regionsexcept for the specific annular region.

The above embodiment was arranged to use the fly's eye lens 14 as anoptical integrator, but it is also possible to use an internalreflection type integrator (e.g., glass rod) as an optical integrator.In this case, the exit plane of the glass rod is not located on thepupil plane 14 of the illumination optical system, but is located on aplane conjugate with the reticle R.

In the above embodiment the laser light source as the exposure lightsource 1 was arranged to emit the linearly polarized light polarized inthe X-direction, but the laser light source, depending upon its type,can emit linearly polarized light polarized in the Z-direction in FIG.1, or a beam in another polarization state. In the case where theexposure light source 1 in FIG. 1 emits light linearly polarized in theY-direction, i.e., light linearly polarized in the Z-direction at thepositions of the birefringent members 12, 13, the birefringent members12, 13 described in the above first and second examples are rotated 90°about the optical axis of illumination system AX2, whereby theillumination light can be obtained in much the same polarization stateas the polarization state shown in FIG. 4C and FIG. 6C (precisely,illumination light in a state resulting from 90° rotation of the stateshown in the two figures).

Alternatively, the polarization controlling member 4 (polarizationcontrolling mechanism) in FIG. 1 may be used to convert theY-directional linear polarization emitted from the exposure light source1, into X-directional linear polarization. This polarization controllingmember 4 can be readily substantialized by a so-called half wavelengthplate. In cases where the exposure light source 1 emits light ofcircular polarization or elliptic polarization, it can also be convertedinto the desired Z-directional linear polarization, similarly using ahalf wavelength plate or a quarter wavelength plate as the polarizationcontrolling member 4.

It is, however, noted that the polarization controlling member 4 is notnecessarily able to convert a beam in an arbitrary polarization stateemitted from the exposure light source 1, into the Z-directionalpolarization without loss in light quantity. Therefore, the exposurelight source 1 needs to generate a beam in a single polarization state(beam that can be converted into linear polarization without loss inlight quantity by a wavelength plate or the like), such as linearpolarization, circular polarization, or elliptic polarization. However,where the intensity of the beam except for the aforementioned singlepolarization state is not so high relative to the total intensity of theillumination light, the adverse effect of the beam except for the singlepolarization state is not so significant on the imaging characteristics,and thus the beam emitted from the exposure light source 1 may containthe beam except for the single polarization state to some extent (e.g.,approximately 20% or less of the total light quantity).

When consideration is given to operating circumstances of the projectionexposure apparatus of the above embodiment, it is not always the best toset the polarization state of the illumination light so that theillumination light distributed in the specific annular region is linearpolarization approximately parallel to the circumferential direction ofthe annular region or so that the specific illumination light isincident as S-polarization to the reticle R. Namely, there is a casewhere it is preferable to adopt normal illumination (illumination with acircular illumination light quantity distribution on the pupil plane 15of the illumination optical system) instead of the annular region,depending upon the pattern on the reticle R to be exposed. In this case,it is sometimes preferable not to use the illumination light in thepolarization state in the above embodiment.

For making the apparatus compatible with such operating conditions aswell, the polarization controlling member 4 in FIG. 1 may be implementedby adopting an element or optical system capable of converting thepolarization state of the beam emitted from the light source such as alaser, into random polarization or the like according to need. This canbe realized, for example, by two polarization beam splitters 4 b, 4 c orthe like as shown in FIG. 10.

FIG. 10 shows a polarization control optical system which can be placedat the position of the polarization controlling member 4 in FIG. 1. Inthis FIG. 10, for example, an illumination beam IL0 (corresponding tothe illumination light IL in FIG. 1) consisting of linearly polarizedlight is incident to a rotatable wavelength plate 4 a consisting of ahalf wavelength plate or quarter wavelength plate. This converts theillumination beam IL0 into an illumination beam IL1 of linearpolarization inclined at 45° from the plane of FIG. 10, or of circularpolarization, and the first polarization beam splitter 4 b divides theillumination beam IL 1 into a beam IL2 of P-polarization component and abeam IL3 of S-polarization component with respect to its dividingsurface. One beam IL2 travels straight upward through the prism 4 b inFIG. 10, and the other beam IL3 is reflected to the right in FIG. 10.

The beam IL2 traveling straight is then incident to the polarizationbeam splitter 4 c and, because of the polarization characteristicsthereof, the beam IL2 travels straight in the polarization beam splitter4 c and then travels as a beam IL4 upward in FIG. 10. On the other hand,the reflected beam 1L3 is reflected by mirrors 4 d, 4 e and then entersthe polarization beam splitter 4 c to be reflected again therein. Thereflected beam IL3 merges with the beam IL4 traveling straight. At thistime, where DL represents each of the spacings between the polarizationbeam splitters 4 b, 4 c and the mirrors 4 d, 4 e, there is the pathlength difference of 2 DL between the two merging beams IL3, IL4. Whenthis path length difference of 2 DL is set longer than the coherentlength of the illumination beam, there is no coherence between the twobeams, so that the merged light can be substantially of randompolarization.

When this polarization control optical system is loaded in theillumination optical system ILS in FIG. 1, the illumination light ILtransmitted thereby is always of random polarization and could be ahindrance to implementation of the polarization state in the aboveembodiment. However, this hindrance will not be caused in principle inthe optical system shown in FIG. 10 because the rotatable wavelengthplate 4 a can be rotated to convert the polarization state of theillumination light IL1 transmitted by the rotatable wavelength plate 4a, into linear polarization the whole of which passes through the firstbeam splitter 4 b. However, some loss of light quantity is essentiallyinevitable due to absorption in the polarization beam splitters 4 b, 4c, reflection loss on the mirrors 4 d, 4 e, and so on, and it is thusoptional to provide a mechanism for retracting the beam splitters 4 b, 4c and rotatable wavelength plate 4 a to outside the optical path of theillumination optical system when there is no need for converting theillumination light into random polarization.

Incidentally, without use of such polarization beam splitters, thefollowing simple method can also offer an effect similar to that by therandom polarization illumination. This can be implemented as follows:the polarization state of the illumination light IL incident to thefirst birefringent member 12 in FIG. 1 is set to polarization in thedirection 45° apart from the X-direction and Z-direction in FIG. 1,whereby the illumination light distributed in the specific annularregion is converted into approximately circular polarization. Therefore,in cases where the projection exposure apparatus of the presentembodiment is used in applications in which the circular polarizationcan be deemed approximately as random polarization, i.e., inapplications in which the imaging performance required is relatively notso high, it is also feasible to achieve the effect similar to that bythe random polarization illumination, by a configuration wherein thepolarization controlling member 4 in FIG. 1 is constructed, for example,of a half wavelength plate whereby the polarization state of theillumination light incident to the first birefringent member 12 is setto polarization in the direction inclined at 45° from the X-axis andZ-axis as described above. It is also feasible to achieve the effectsimilar to that by the random polarization illumination, by a similarconfiguration wherein the polarization controlling member 4 isconstructed, for example, of a quarter wavelength plate whereby thepolarization state of the illumination light incident to the firstbirefringent member 12 is set to circular polarization.

Alternatively, it is also feasible to achieve the effect similar to thatby the random polarization illumination, by a configuration wherein therelation between the two birefringent members 12, 13 and the directionof linear polarization of the illumination light is rotated, forexample, by 45° by a rotating mechanism 101 capable of wholly rotatingthe first birefringent member 12 and the second birefringent member 13in FIG. 1 about the optical axis of illumination system AX2 being theoptical axis of the illumination optical system ILS.

Incidentally, in the case of the normal illumination, there are alsocases wherein the polarization state thereof is preferably set to linearpolarization in a predetermined direction. For making the projectionexposure apparatus of the above embodiment compatible with thisillumination condition, the apparatus is provided with a rotatingmechanism 101 capable of wholly rotating each of the birefringentmembers, such as the first birefringent member 12 and the secondbirefringent member 13 in FIG. 1, independently about the optical axisof illumination system AX2, and the direction of rotation of eachbirefringent member is set so that the fast axis (or slow axis) of eachbirefringent member is in parallel with the direction of linearpolarization of the illumination light. In this case, the illuminationlight travels through each birefringent member, without being affectedby the converting action of the polarization state at all, and emergesas keeping the linear polarization at the time of incidence.

For setting the polarization in the linear polarization state in the onepredetermined direction, it can also be implemented by wholly retractingthe first birefringent member 12 and the second birefringent member 13and others to outside the optical path of the illumination opticalsystem. Namely, the setting of the linear polarization state in the onepredetermined direction may be implemented by providing a replacingmechanism 102 and replacing the birefringent members and others alltogether thereby. When the apparatus is provided with the replacingmechanism 102, it is also possible to adopt a configuration wherein thereplacing mechanism 102 is arranged to set plural sets of birefringentmember groups therein and wherein they can be replaceably arranged onthe position on the optical axis of illumination system AX2. In thiscase, it is a matter of course that each birefringent member group ispreferably provided with the characteristics of converting theillumination light into linear polarization along the circumferentialdirection of the specific annular region, in the specific annular regionwith the outside radius and inside radius different among the groups.

Incidentally, a preferred case to use the illumination light of linearpolarization in the one predetermined direction as described above is,for example, exposure of a phase shift reticle of a spatial frequencymodulation type with a pattern aligned along a direction. In this case,in order to further improve the resolution and depth of focus of thepattern to be transferred by exposure, the coherence factor (σ value) ofthe illumination light is preferably not more than about 0.4.

When consideration is given again to the action of the birefringentmembers according to the present invention (first birefringent member 12and second birefringent member 13) with reference to FIG. 4C and FIG.6C, it is apparent from the two figures that the first example (FIG. 4C)and the second example (FIG. 6C) of the first birefringent member 12 andthe second birefringent member 13 cause little influence on thepolarization state of the illumination light distributed inside a circle(not shown) with the center on the optical axis of the illuminationoptical system (X=0, Z=0) and with the radius approximately equal tohalf of the radius of the exterior circle C1 of the specific annularregion.

Supposing the radius of the exterior circle C1 is equivalent, forexample, to 0.9 as illumination σ (σ value), the first birefringentmember 12 and second birefringent member 13 emit the incident linearpolarization in the X-direction, while keeping it almost in the originalpolarization state, within the range of the illumination beam ofillumination σ=0.45. When linear polarization in the Z-direction(Z-polarization) is made incident to the first birefringent member 12,the polarization state of the illumination beam of approximately theabove illumination σ=0.45 can be Z-polarization in the beam emitted fromthe second birefringent member 13.

Therefore, when the birefringent members as in the first and secondexamples (the first birefringent member 12 and second birefringentmember 13) are used, the aforementioned polarization controlling member4 or the like is used to switch the polarization direction of theincident light to the birefringent members, without retracting them tooutside the optical path of the illumination optical system, whereby itbecomes feasible to realize the illumination light being theillumination beam with the illumination σ of not more than about 0.4 andbeing light polarized in the X-direction or in the Z-direction(polarization in the X-direction or in the Y-direction, respectively, onthe reticle R in FIG. 1), suitable for illumination onto the spatialfrequency modulation type phase shift reticle.

In this case, it is also a matter of course that, in order to limit theillumination σ to about 0.4, it is preferable to use such a diffractiveoptical element 9 a that the direction characteristic of the generateddiffracted light is an angular distribution corresponding thereto. Thispermits the apparatus to form illumination beams in a variety ofpractical polarization states without provision of the whole replacingmechanism, which is also the advantage of the present invention.

Next, an example of production steps of semiconductor devices using theprojection exposure apparatus of the above embodiment will be describedwith reference to FIG. 11.

FIG. 11 shows an example of production steps of semiconductor devicesand in this FIG. 11, a wafer W is first made of a silicon semiconductoror the like. Thereafter, a photoresist is applied onto the wafer W (stepS10) and in the next step S12, a reticle (assumed to be R1) is loaded onthe reticle stage of the projection exposure apparatus of the aboveembodiment (FIG. 1), the wafer W is loaded on the wafer stage, and apattern on the reticle R1 (indicated by symbol A) is transferred (toeffect exposure) into all shot areas SE on the wafer W by the scanningexposure method. On this occasion double exposure is carried outaccording to need. The wafer W is, for example, a wafer with thediameter of 300 mm (12-inch wafer), and the size of each shot area SEis, for example, a rectangular region with the width of 25 mm in thenon-scanning direction and the width of 33 mm in the scanning direction.In the next step S14, development, etching, ion implantation, and so onare carried out to form a predetermined pattern in each shot area SE onthe wafer W.

In the next step S16, a photoresist is applied onto the wafer W and instep S18 thereafter, a reticle (assumed to be R2) is loaded on thereticle stage of the projection exposure apparatus of the aboveembodiment (FIG. 1), the wafer W is loaded on the wafer stage, and apattern on the reticle R2 (indicated by symbol B) is transferred (toeffect exposure) into each shot area SE on the wafer W by the scanningexposure method. In next step S20, development, etching, ionimplantation, and so on of the wafer W are carried out to form apredetermined pattern in each shot area on the wafer W.

The above exposure step to pattern forming step (step S16 to step S20)are repeated the number of times necessary for production of desiredsemiconductor devices. Then semiconductor devices SP as products arefabricated through a dicing step (step S22) of separating chips CP onthe wafer W from each other, a bonding step, and a packaging step andothers (step S24).

Since the device fabrication method of the present example involvescarrying out the exposure by the projection exposure apparatus of theabove embodiment, the exposure step enables the reticle to beilluminated with the illumination light (exposure beam) in thepredetermined polarization state with increased efficiency ofutilization thereof. Therefore, the resolution and others are improvedfor periodic patterns with a fine pitch or the like, so thathigher-integration and higher-performance semiconductor integratedcircuits can be fabricated at low cost and at high throughput.

The projection exposure apparatus of the above embodiment can beproduced as follows: the illumination optical system and projectionoptical system composed of a plurality of lenses are incorporated in themain body of the exposure apparatus, optical adjustment is carried outfor the optics, the reticle stage and wafer stage comprised of a numberof mechanical parts are attached to the main body of the exposureapparatus, wires and tubes are connected thereto, and overallconditioning processes (electric adjustment, confirmation of operation,etc.) are further carried out. The production of the projection exposureapparatus is preferably carried out in a clean room in which thetemperature, cleanliness, etc. are controlled.

The present invention is applicable not only to the projection exposureapparatus of the scanning exposure type, but also to the projectionexposure apparatus of the full exposure type such as steppers. Themagnification of the projection optical system used may be ademagnification rate, a 1:1 magnification, or an enlargementmagnification. Furthermore, the present invention is also applicable,for example, to the liquid immersion type exposure apparatus asdisclosed in International Publication (WO) 99/49504 or the like.

The usage of the projection exposure apparatus of the present inventionis not limited to the exposure apparatus for fabrication ofsemiconductor devices, but it is also commonly applicable, for example,to exposure apparatus for display devices such as liquid crystal displaydevices formed on rectangular glass plates, or plasma displays, and toexposure apparatus for fabricating various devices such as image pickupdevices (CCDs or the like), micromachines, thin film magnetic heads, andDNA chips. Furthermore, the present invention is also applicable to theexposure step (exposure apparatus) in production of masks (photomasksincluding X-ray masks, reticles, etc.) with mask patterns for variousdevices by the photolithography step.

It is needless to mention that the illumination optical system (2-20) inthe projection exposure apparatus in the aforementioned embodiment isalso applicable to the illumination optical apparatus for illuminatingthe first object such as the reticle R.

It is a matter of course that the present invention is not limited tothe above embodiment and can be modified in a variety of configurationswithout departing from the spirit and scope of the present invention.The entire disclosure of Japanese Patent Application No. 2003-367963filed Oct. 28, 2003, including the specification, scope of claims,drawings, and abstract is incorporated by reference herein in itsentirety.

The device fabrication method of the present invention enablesenhancement of utilization efficiency of the exposure beam (illuminationlight) and permits a predetermined pattern to be formed with highaccuracy. Therefore, it permits various devices such as semiconductorintegrated circuits to be fabricated with high accuracy and highprocessing performance (throughput).

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedfor inclusion within the scope of the following claims.

What is claimed is:
 1. An illumination optical apparatus forilluminating a pattern on a mask with illumination light, comprising: anillumination system including a birefringent member made of birefringentmaterial, configured to illuminate the pattern with the illuminationlight which enters into the birefringent member and has a polarizationstate of a substantially single linearly polarization component as aprinciple component, in a polarization state in which a principlecomponent is S polarized light, through a pupil plane of theillumination optical system, wherein a first thickness of thebirefringent member in an optical path of a first illumination lightwhich passes through a first position of the pupil plane is differentfrom a second thickness of the birefringent member in an optical path ofa second illumination light which passes through a second position ofthe pupil plane.